Green post-harvest processing method for citrus fruits

Abstract

The present invention belongs to the technical field of fresh agricultural product storage and preservation, and specifically relates to a green postharvest processing method for citrus fruit. In particular, the present invention utilizes green, natural plant materials to reduce the use of chemical fungicides, promote postharvest micro-wound healing, reduce rot and loss, and minimize postharvest water loss. This method is suitable for the green postharvest production of citrus fruit.

Description

Technical Field

[0001] The present invention belongs to the technical field of storage and preservation of fresh agricultural products, specifically to a method for utilizing green, natural plant materials to reduce the use of chemical fungicides, promote healing of postharvest micro-wounds in citrus fruits, reduce rot and loss of citrus fruits, and reduce postharvest water loss. This method is suitable for the green production of postharvest citrus fruits. Background Art

[0002] my country is a major citrus producer, ranking first in the world in both citrus cultivation area and production. In 2021, my country's total citrus production of all types reached 55.9561 million tons. Over 90% of my country's citrus is consumed fresh. Due to the high water content of citrus fruits, they are highly susceptible to fungal infection during harvesting, storage, and transportation. Furthermore, improper production practices can easily cause mechanical damage to the fruit, damaging the surface and accelerating fungal infection, leading to frequent rot. During postharvest commercial processing, fruits with significant mechanical wounds are sorted in advance. However, fruits with minor wounds that are difficult to detect visually are processed and stored alongside healthy fruits, ultimately entering the market. These minor wounds are susceptible to infection and spread of postharvest diseases during storage, and their quality is more likely to deteriorate than healthy fruits. Therefore, postharvest citrus processing methods must not only ensure the preservation of healthy fruits, but also protect and preserve the minor wounds and accelerate wound healing.

[0003] Citrus postharvest diseases are most severe with penicillium and green mold caused by Penicillium italicum and Penicillium digitatum. Sour rot caused by Geotrichum candidum, stem rot caused by Fusarium spp., anthracnose caused by Periphyton solani, and black rot caused by Alternaria alternata also occur. Disease control is primarily achieved with chemical agents, such as prochloraz, imazalil, and sodium o-phenylphenol. These agents often require multiple treatments to address a variety of diseases, leading to excessive use of these agents. With increasing consumer awareness of food safety and environmental protection, the use of chemical preservatives will inevitably decrease in line with market demand, or even be replaced by safer and greener preservation methods. In addition to accelerating pathogen infection, postharvest mechanical damage can negatively impact the appearance and physiological qualities of the fruit, causing color changes, decreased firmness, and accelerated softening. Mechanical damage to the fruit surface also accelerates postharvest water loss, increases respiration rate, and accelerates fruit aging. Therefore, the rapid healing of micro-wounds after fruit harvest is of great significance for maintaining the integrity of fruit tissue, reducing the fruit decay rate, maintaining the freshness of the fruit, and extending the shelf life. Summary of the Invention

[0004] The purpose of the present invention is to provide a green post-harvest treatment method for citrus fruits, which significantly inhibits the post-harvest decay rate of healthy citrus fruits and slightly damaged fruits without damaging the storage quality and commercial quality of the fruits, significantly delays the water loss rate of slightly damaged fruits during the post-harvest storage period, and promotes the healing of minor wounds on the fruit epidermis.

[0005] Oil meal is an agricultural waste byproduct produced after oil extraction from camellia oleifera. In practical applications, the inventors have discovered that soaked solutions or extracts of camellia oleifera meal have a strong inhibitory effect on various postharvest pathogens of citrus (Penicillium italicum, Penicillium digitatum, Geotrichum candidum, Fusarium, Periphyton, and Alternaria), effectively reducing the postharvest decay rate of citrus while having no adverse effects on the intrinsic quality of commercially mature citrus fruits. Furthermore, the inventors have discovered that treating citrus with soaked solutions or extracts of camellia oleifera meal can increase lignin accumulation and peroxidase activity in wounded areas of citrus fruits, aiding the healing of micro-wounds on the fruit surface and improving resistance. This can effectively reduce postharvest decay and excessive water loss in wounded fruit, thereby minimizing storage losses.

[0006] Therefore, the present application provides the following invention:

[0007] In one aspect, the present application provides a method for processing citrus fruit, comprising: immersing the fruit in a soaking liquid or extract of camellia oil meal for 1-3 minutes, wherein the soaking liquid or extract of camellia oil meal is an aqueous solution at a temperature of 30-60°C; optionally, the method further comprises: drying the citrus fruit (e.g., air-drying or oven-drying), and then bagging or storing it normally.

[0008] In the present invention, "citrus" refers to plants of the genus Citrus in the Rutaceae family, including but not limited to navel oranges (such as London late navel oranges, Newhall navel oranges, summer oranges), sugar oranges (sugar oranges), ponkan, and Wenzhou mandarin oranges.

[0009] In the present invention, "camellia oleifera meal" refers to the residue produced after the camellia oleifera seeds are squeezed or leached to extract the oil, also known as "tea seed meal", and camellia oleifera refers to plants of the Camellia genus of the Theaceae family.

[0010] The tea seed meal soaking solution can be prepared by a method comprising the following steps: soaking the tea seed meal in hot water at 30-60°C (e.g., 30°C, 40°C, 42°C, 50°C, 52°C, or 60°C) for 0-3 hours (e.g., 0.5 hours, 1 hour, 2 hours, or 3 hours). To facilitate post-processing, the tea seed meal can be processed into small pieces and placed in a gauze bag. In certain embodiments, the weight ratio of the tea seed meal to water can be 1:5 to 1:15 (W / W), for example, 1:10 (W / W).

[0011] Camellia oil meal extract can be produced by a method comprising the following steps: mixing camellia oil meal powder with water, extracting for 1-2 hours (e.g., 1.5 hours), removing the camellia oil meal powder to obtain a liquid; and uniformly mixing the liquid with hot water at 30-60°C (e.g., 30°C, 40°C, 42°C, 50°C, 52°C, or 60°C). Camellia oil meal powder can be obtained by pulverizing camellia oil meal and then sieving it. In certain embodiments, the camellia oil meal powder is sized to pass through a 50-mesh sieve. The size of the camellia oil meal powder has a certain impact on the extraction efficiency. In certain embodiments, the weight ratio of camellia oil meal powder to extraction water is 1:3 to 1:5 (W / W), for example, 1:4 (W / W). In certain embodiments, extraction is performed at 25-40°C (e.g., 25-30°C, 30-35°C, or 35-40°C).

[0012] The camellia oil meal powder can be removed by filtration or centrifugation to obtain a filtrate or supernatant. In certain embodiments, the liquid obtained after removing the camellia oil meal powder is mixed with hot water at a ratio of 1:80 to 1:90 (V / V).

[0013] In another aspect, the present application provides the use of the water soaking liquid or water extract of camellia oil meal prepared by the method described above for preserving citrus fruits or improving the internal and / or external quality of citrus fruits.

[0014] In certain embodiments, the preservation is post-harvest preservation.

[0015] In the present invention, the term "fresh-keeping" refers to prolonging the storage period or shelf life (particularly the shelf life at room temperature) of the fruit.

[0016] In certain embodiments, the water soak or water extract of the camellia oleifera meal can be used for one or more of the following purposes: inhibiting the post-harvest decay rate of healthy citrus fruits or slightly wounded fruits, slowing down the water loss rate of citrus slightly wounded fruits during the post-harvest storage period, promoting the healing of micro-wounds on the epidermis of citrus fruits, slowing down the loss of firmness of citrus fruits, inhibiting post-harvest pathogens of citrus (such as Penicillium digitatum, Penicillium italicum, Geotrichum candidum, Fusarium, Aspergillus niger, Alternaria alternata, etc.), and slowing down the color change of the fruit surface.

[0017] In the present invention, "micro-wounds" refer to tiny wounds that cannot be identified with the naked eye and can be identified by methods and equipment commonly used in the art for detecting plant product damage.

[0018] In certain embodiments, the citrus is selected from the group consisting of navel oranges (eg, London late navel oranges, Newhall navel oranges, summer oranges), sugar oranges, ponkan oranges, and satsuma oranges.

[0019] In certain embodiments, the use is achieved by the method of treating citrus fruit as described above.

[0020] The present application also provides a citrus fruit preservative, which comprises a water soak or water extract of camellia oil meal prepared by the method described above.

[0021] Beneficial effects

[0022] The present invention utilizes a water-soaked or water-extracted tea oil cake to significantly inhibit the postharvest decay rate of healthy citrus fruit and slightly damaged fruit, without compromising the fruit's storage or commercial quality. It also significantly slows the rate of water loss during postharvest storage of slightly damaged fruit and promotes the healing of minor wounds on the fruit's epidermis. The water-soaked or water-extracted tea oil cake can replace chemical preservatives, making it safer and more environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 The results show the incidence of green mold in healthy Lunwan navel orange fruits in the control group and the treatment group of Example 1.

[0024] Figure 2 The graph shows the weight loss rate of healthy Lunwan navel orange fruits in the control group and the treatment group of Example 1.

[0025] Figure 3 The soluble solids and titratable acid contents of healthy Lunwan navel orange fruits in the control group and the treatment group of Example 1 are shown.

[0026] Figure 4 The color changes of healthy Lunwan navel orange fruits in the control group and the treatment group of Example 1 are shown.

[0027] Figure 5 The peel hardness of healthy Lunwan navel orange fruits in the control group and the treatment group of Example 1 is shown.

[0028] Figure 6 The water content of healthy Lunwan navel orange fruits in the control group and the treatment group of Example 1 is shown.

[0029] Figure 7 The respiratory intensity of healthy Lunwan navel orange fruits in the control group and the treatment group of Example 1 is shown.

[0030] Figure 8 The rot rates of the Weichuanlun late navel orange fruits in the control group and the treatment group of Example 2 are shown.

[0031] Figure 9 The respiratory intensity of the Weichuanlun late navel orange fruits in the control group and the treatment group of Example 2 is shown.

[0032] Figure 10 The solid-acid ratio of the Weichuanlun late navel orange fruits in the control group and the treatment group of Example 2 is shown.

[0033] Figure 11 The lignin content of the Weichuanlun late navel orange fruits in the control group and the treatment group of Example 2 is shown.

[0034] Figure 12 The weight loss rate of the minimally invasive summer orange fruits in the control group and the treatment group of Example 3 is shown.

[0035] Figure 13 The lignin content of the minimally invasive summer orange fruits in the control group and the treatment group of Example 3 is shown.

[0036] Figure 14A and Figure 14B The peroxidase activity of the minimally invasive summer orange fruits in the control group and the treatment group of Example 3 is shown.

[0037] Figure 15 The rot rates of the Wenzhou mandarins in the control group and the treatment group of Example 4 are shown.

[0038] Figure 16 The weight loss rates of the Wenzhou mandarins in the control group and the treatment group of Example 4 are shown.

[0039] Figure 17 The peel hardness of the Wenzhou mandarin oranges in the control group and the treatment group of Example 4 is shown.

[0040] Figure 18 The results show the inhibitory effect of the oil cake water extract in Example 5 on various post-harvest pathogens of citrus.

[0041] Figure 19 The results show the inhibitory effect of the oil cake water extracts with different pH values ​​on Penicillium digitatum in Example 6.

[0042] Figure 20 The antibacterial abilities of the different extracts tested in the plate antibacterial test in Example 7 are shown. DETAILED DESCRIPTION

[0043] The embodiments of the present invention will be described in detail below with reference to the examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present invention and should not be construed as limiting the scope of the invention. Where specific conditions are not specified in the examples, the methods were performed according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturers of the reagents or instruments are not specified, they are all conventional products that can be obtained commercially.

[0044] The main physiological index determination methods in each embodiment of the present invention are as follows

[0045] 1. Determination of rot rate (green mold incidence)

[0046] The number of rotten fruits / fruits infected with green mold was determined using a visual counting method. Fruits with signs of mold on the stem or the presence of rotten spots or fungal hyphae on the fruit surface were considered rotten. Each treatment had three replicates, with 70 fruits per replicate. The rot rate was counted at regular intervals and the data were recorded to calculate the fruit rot rate.

[0047] Fruit rot rate (%) = total number of rotten fruits in each group / 70 × 100

[0048] 2. Weight loss rate: 20 fruits from each treatment were selected and numbered. The weight before storage (W0) was measured using a 1% electronic balance (model: MP31001, Shanghai Hengping Scientific Instrument Co., Ltd.). The weight (W) was then measured at regular intervals. The data were recorded and the weight loss rate of the fruit was calculated.

[0049] Fruit water loss rate (%) = (W0-W) / W0×100

[0050] 3. Determination of fruit soluble solids (TSS) and titratable acid (TA)

[0051] Twelve fruits from each treatment were selected for juice extraction, with three replicates of four fruits per group. The soluble solids content of the juice was measured using a PAL-1 pocket refractometer (Atago, Japan). The juice was diluted 100-fold, mixed, and titratable acidity was measured using a digital acidometer (GMK-835, G-WON HITECH CO, LTD, Korea).

[0052] 4. Fruit hardness measurement

[0053] Twelve fruit samples from each treatment group were selected for firmness testing at each storage stage. A texture analyzer (TA-XT2i Plus, Stable Micro System, UK) was used to test three points at the equator of the fruit. The probe had a diameter of 2.0 mm, a penetration rate of 10 mm / s, and a final penetration depth of 20 mm. The results were expressed as firmness (force at 1 mm).

[0054] 5. Respiratory intensity measurement

[0055] Nine fruits were selected for each treatment, with three replicates, each group of three. The fruits were weighed, sealed in a fresh-keeping box, and placed at room temperature for 1 hour. A CO2 sensor was used to detect the real-time CO2 concentration in the sealed box, with readings taken every 30 minutes. The change in CO2 concentration per unit time was calculated. The unit of fruit respiration rate is mg / (kg·h)

[0056] 6. Fruit moisture content determination

[0057] Six fruits were selected from each treatment and their fresh weight W0 was weighed. The slices were then placed in a Septree dryer and dried at 70°C until the weight was constant, which was recorded as the dry weight W. The moisture content of the fruits was then calculated and the average value was taken.

[0058] Fruit moisture content (%) = (W0-W) / W0×100

[0059] Example 1: Oil cake hot solution treatment of healthy Lunwan navel orange fruits

[0060] This example uses the Cailunwan navel orange from Zigui as the test object. After soaking the camellia oil meal in 50°C hot water for 3 hours at a ratio of 1:10 (W / W), the Lunwan navel orange fruit is soaked in the hot solution for 1 minute. After the liquid on the surface of the fruit is dried, it is bagged and stored. The control group is heat-treated with 50°C water for 1 minute, dried and bagged for storage. Every 15 days, the fruit's green mold incidence, weight loss rate, soluble solids content, titratable acid content, color change, hardness, moisture content and respiration intensity are measured at a node. The test lasts for 60 consecutive days, of which the green mold incidence is measured for a total of 75 days. (CK is the control group, and YC is the oil meal treatment group)

[0061] 1. Green mold incidence:

[0062] like Figure 1 As shown in the results, after 60 days of storage at room temperature, the green mold incidence rate of the control group was 17.14%, while that of the treated group was 5.24%. The rot rate of the treated group was significantly lower than that of the control group.

[0063] 2. Weight loss rate:

[0064] like Figure 2 As shown in the figure, after storage at room temperature for 60 days, the average weight loss rate of the fruits in the control group was 5.34%, while that in the treated group was 5.09%.

[0065] 3. Soluble solids and titratable acid content:

[0066] like Figure 3 As shown in the results, after 60 days of storage at room temperature, the average soluble solids and titratable acid contents of the fruit in the control group were 12.50% and 0.94%, respectively, while those in the treated group were 12.30% and 1.02%, respectively. There were no significant differences in soluble solids and titratable acid content between the control and treated groups, and the edible quality of the fruit was not significantly affected.

[0067] 4. Color change:

[0068] like Figure 4 As shown in the figure, ΔE represents the trend of the overall color change of the fruit. Compared with the control group, the trend of the fruit surface color change in the treatment group slowed down significantly within 60 days.

[0069] 5. Peel hardness:

[0070] like Figure 5As shown in the figure, after 60 days of storage at room temperature, the fruit peel hardness of the control group was significantly lower than that of the treatment group. The average fruit peel hardness of the control group was 353.38 (force at 1mm), and that of the treatment group was 394.14 (force at 1mm).

[0071] 6. Moisture content:

[0072] like Figure 6 As shown in the figure, after 60 days of storage at room temperature, there was little difference in the water content between the control group and the treated group, and the edible quality of the fruit was not significantly affected.

[0073] 7. Breathing intensity:

[0074] like Figure 7 As shown in the figure, the respiration intensity of the treated group's fruit during storage was significantly lower than that of the control group. The level of respiration intensity represents the strength of the respiration inside the fruit. The lower the respiration, the less sugar and acid metabolism inside the fruit, and the better the internal quality can be maintained.

[0075] Example 2: Treatment of Micro-Cream Late Navel Orange Fruits with Hot Solution of Oil Cake

[0076] In this example, Zigui Cailun Late Navel Oranges were used as test subjects. A sterilized toothpick bundle was used to poke holes on the equatorial surface of the fruit to simulate micro-trauma on the fruit surface. Each wound site had a total of 9 holes with a diameter of 1 mm and a depth of 3 mm, with 3 wounds per fruit.

[0077] After soaking camellia oil meal in 52°C hot water at a ratio of 1:10 (W / W) for 2 hours, the Lunwan navel orange fruit was soaked in the hot solution for 1 minute. After the liquid on the fruit surface dried, it was stored at room temperature. The control group was treated with room temperature water for 1 minute, dried, and stored at room temperature. The incidence of green mold on the fruit was measured at a node every 4 days for 28 consecutive days; the soluble solids content, titratable acid content, and respiration rate were measured at a node every 4 days for 12 consecutive days. (CK is the control group, T is the oil meal treatment group)

[0078] 1. Decay rate

[0079] like Figure 8 As shown in the figure, after 28 days of storage at room temperature, the average rot rate of the control group was 68.33%, while that of the treated group was 16.11%. Throughout the storage period, the rot rate of the treated group was significantly lower than that of the control group.

[0080] 2. Breathing intensity

[0081] like Figure 9As shown, the overall respiration rate of the treated fruit was similar to that of the control fruit during storage, with a significant decrease only on day 8. Respiration rate indicates the strength of respiration within the fruit. Lower respiration indicates reduced sugar and acid metabolism within the fruit, leading to better maintenance of internal quality.

[0082] 3. Solid-acid ratio (soluble solids / titratable acid)

[0083] like Figure 10 As shown, the solid-acid ratio of both the treated and control groups showed a downward and then upward trend during storage, with no significant difference between the two groups throughout the storage period. The solid-acid ratio is an important indicator of citrus fruit maturity and commercial quality, and the treatment group had no adverse effects on commercial quality.

[0084] 4. Lignin content (observed by section staining)

[0085] like Figure 11 As shown in the figure, staining of sections from the wound site on the 12th day of storage revealed significant lignin accumulation around the wound site. The treated group showed a darker, wider area than the control group. The scale bar in the figure represents 50 μm. Lignin is a crucial component of plant cell walls, and its accumulation at the wound site is a key indicator of postharvest wound healing. Phloroglucinol staining can be used to monitor lignin accumulation at the wound site.

[0086] Example 3: Oil cake hot solution treatment of minimally invasive summer orange fruit

[0087] This example uses summer oranges as the test subject. Camellia oil meal was soaked in 52°C hot water at a ratio of 1:10 (W / W) for 2 hours. Summer orange fruits were then soaked in the hot solution for 1 minute. After the liquid on the fruit surface dried, they were stored at room temperature. The control group was treated with room temperature water for 1 minute, dried, and stored at room temperature. The fruit weight loss rate, lignin content, and peroxidase activity were measured at each node every 4 days for 12 consecutive days. (CK is the control group, T is the oil meal treatment group)

[0088] 1. Weight loss rate

[0089] like Figure 12 As shown in the figure, after 12 days of storage at room temperature, the average weight loss rate of the control group was 4.95%, while that of the treated group was 4.28%. The weight loss rate of the treated group was significantly lower than that of the control group throughout the storage period, and was extremely significantly lower than that of the control group on the 12th day.

[0090] 2. Lignin content

[0091] like Figure 13 As shown in the figure, on the 8th day of storage, microscopic observation revealed lignin enrichment in the wound site of the treatment group. The scale bar in the figure is 20 μm. On the 12th day of storage, the lignin content in the treatment group was higher than that in the control group.

[0092] 3. Peroxidase activity (POD, CAT)

[0093] like Figure 14A and Figure 14B As shown, after 12 days of storage at room temperature, the POD activity of the treated group was higher than that of the control group throughout the storage period, with extremely significant differences at 4 and 8 days. CAT activity in the treated group was significantly higher than that of the control group at 4 days of storage and extremely significantly higher at 12 days. POD is a key enzyme regulating lignin synthesis in citrus fruit; CAT is a marker enzyme for hydrogen peroxide scavenging and an important indicator of fruit's anti-aging capacity.

[0094] Example 4: Treatment of healthy Wenzhou mandarin oranges with oil cake water extract

[0095] In this example, Wenzhou mandarin oranges were used as the test subjects. The oil meal powder was mixed with distilled water at a ratio of 1:4 (W / V), and filtered after extraction for 1.5 hours. The filtrate was added to 42°C hot water at a ratio of 1:80 (V / V) and mixed. The Wenzhou mandarin orange fruits were immersed in the hot solution for 1 minute. After the liquid on the surface of the fruit dried, they were stored at room temperature. The control group was treated with room temperature water for 1 minute, dried and stored at room temperature, and the positive control was treated with 40mg / L and 80mg / L prochloraz hot soaking (42°C). The fruit weight loss rate and rot rate were measured at a node every 7 days for 28 consecutive days. The peel hardness was measured at the end of storage (42 days). (CK is the control group, and RC is the oil meal treatment group)

[0096] 1. Decay rate

[0097] like Figure 15 As shown, after 28 days of storage at room temperature, the average fruit decay rate in the control group was 9.58%, while the average decay rate in the prochloraz-positive control group was 2.92% (40 mg / L) and 2.08% (80 mg / L), respectively, compared to 3.33% in the treated group. Throughout the storage period, the decay rate in the treated group was significantly lower than that in the control group and showed no significant difference from the positive control group. This suggests that oil-meal treatment can achieve a similar preservative effect as chemical agents.

[0098] 2. Weight loss rate

[0099] like Figure 16 As shown, after 28 days of storage at room temperature after treatment, the average weight loss of the fruit in the control group was 14.72%, the average weight loss in the prochloraz-positive control group was 14.98% (40 mg / L) and 14.84% (80 mg / L), and the weight loss in the treated group was 14.18%. Throughout the storage period, the weight loss rate of the treated group was lower than that of the other groups and did not differ significantly from the control group. Only at the initial stage of storage did a significant difference appear between the treated group and the 80 mg / L prochloraz-positive control group.

[0100] 3. Peel hardness

[0101] like Figure 17 As shown, after 42 days of storage at room temperature, the fruit peel hardness of the control group was 111.55 (force at 1 mm), the prochloraz positive control group was 143.58 (force at 1 mm) (40 mg / L) and 142.01 (force at 1 mm) (80 mg / L), and the treatment group was 139.53 (force at 1 mm). The fruit peel hardness of the treatment group was significantly higher than that of the control group at the end of storage, and there was no significant difference between the treatment group and the positive control group, indicating that the effect of oil meal treatment on delaying the decline of fruit firmness is similar to that of chemical agents.

[0102] Example 5: Verification of the inhibitory effect of oil cake water extract on various post-harvest pathogens of citrus (Penicillium italicum, Penicillium digitatum, Geotrichum candidum, Fusarium spp., Periphyton spp., and Alternaria spp.)

[0103] This example uses a plate antibacterial method for verification. Oil meal powder and distilled water were mixed at a ratio of 1:4 (W / V), extracted at 25-40°C for 1.5 hours, and then centrifuged to obtain a supernatant. The supernatant was added to PDA culture medium at a ratio of 1:50 (V / V) to prepare a drug-containing culture medium. After mixing evenly, the cultured bacterial block was plated. After standing and solidifying, a bacterial block with a diameter of 8 mm was taken from the cultured bacterial block and placed in the center of the plate with the mycelium side facing down. After incubation at 25°C for 5 days, the colony diameter was measured using the cross-hatch method. A pure PDA culture medium plate was used as a blank control (CK).

[0104] like Figure 18 As shown in the results, the oil meal water extract has a good inhibitory effect on three post-harvest pathogens: Penicillium digitatum (green mold), Penicillium italicum (penicillium), and Geotrichum candidum (sour rot). The appropriate effective concentration can completely inhibit the spread and growth of the colony; it also has a certain inhibitory effect on Fusarium (stem rot), Colletotrichum spp. (anthracnose), and Alternaria alternata (black rot).

[0105] Example 6: Verification of the inhibitory effect of oil cake water extracts with different pH values ​​on Penicillium digitatum

[0106] This example uses a plate antibacterial method for verification. Oil meal powder and distilled water were mixed under different pH conditions, extracted for 0.5 h, and then centrifuged to obtain a supernatant. The supernatant was added to PDA culture medium at the same ratio of 1:50 (V / V) to prepare a drug-containing culture medium. After mixing evenly, the culture was plated and allowed to stand for solidification. An 8 mm diameter bacterial block was taken from the cultured Penicillium digitatum block and placed in the center of the plate with the mycelium facing down. After incubation at 28°C for 4 days, the colony diameter was measured using the cross-hatch method. A plate containing the same amount of NaCl solution at different pH values ​​was used as a blank control (CK).

[0107] like Figure 19As shown in the table, plate antibacterial tests examined the antibacterial activity of different extracts. Extracts with the same effective concentration and different pH values ​​had no significant difference in their antibacterial activity against Penicillium digitatum, but the inhibitory effect under weakly alkaline conditions was slightly better than those at pH 10 and pH 12. In actual production, the effect of pH during extraction on the antibacterial activity of oil meal is not significant.

[0108] Example 7: Column chromatography to crudely separate the oil meal methanol extract

[0109] In this example, AB-8 macroporous adsorption resin column chromatography was used to crudely separate the methanol extract of the oil meal. The oil meal was ultrasonically extracted with methanol at a 1:4 (w / v) ratio for 1 hour at a temperature of 25-40°C. The supernatant was centrifuged and concentrated to obtain brown syrup, which was filtered through a 0.22 μm nylon filter membrane. The concentrated solution was then chromatographed on an AB-8 macroporous resin column using a stepwise gradient of ethanol and water (v / v ratios of 0:100, 30:70, 70:30, and 100:0). The second subfraction contained flavonoids as its primary component, while the third subfraction contained total saponins as its primary component.

[0110] The Oxford cup plate inhibition method was used to test the inhibitory ability of each sub-fraction eluate against Penicillium digitatum. PDA culture medium was used for plating, and the culture dish was a 6 cm dish. After the culture medium was allowed to stand and solidify, 100 μL of 10 6 Spread the plate with a 0.5 CFU / mL Penicillium digitatum solution. After spreading evenly, place a sterilized Oxford cup in the center of the plate and add 150 μL of each subfraction eluate to the cup. After incubation at 27°C for 5 days, measure the diameter of the inhibition zone using the cross-hatch method.

[0111] like Figure 20 As shown, plate inhibition tests examined the antibacterial activity of different extracts. The inhibitory activity of the eluates from the subfractions against Penicillium digitatum varied significantly. The third subfraction exhibited the strongest inhibitory activity against Penicillium digitatum, followed by the second subfraction. The fourth subfraction exhibited relatively weak inhibition, and the first subfraction exhibited minimal inhibition. It is speculated that the active ingredients in the oil cake that inhibit postharvest citrus pathogens are primarily saponins and flavonoids.

[0112] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. Use of a water soak or water extract of camellia oil meal for preserving citrus fruit, wherein the preservation is post-harvest preservation, and the use is selected from one or more of the following: delaying the weight loss rate of slightly damaged citrus fruit during post-harvest storage, delaying the loss of firmness of citrus fruit, and delaying the change in color of the fruit surface; The water soaking liquid of the camellia oil meal is prepared by a method comprising the following steps: soaking the camellia oil meal in 42-52° C. hot water for 0.5-3 h; The aqueous extract of camellia oil meal is prepared by a method comprising the following steps: mixing camellia oil meal powder with water, extracting for 1-2 h, removing camellia oil meal powder to obtain a liquid; and uniformly mixing the liquid with 42-52 ° C hot water; The use is achieved by a method comprising the following steps: The fruits are immersed in the soaking liquid or extract of camellia oil cake at 42-52° C. for 1-3 minutes.

2. The use according to claim 1, characterized in that: The citrus is selected from the group consisting of navel orange, sugar orange, ponkan, and satsuma orange.

3. The use according to claim 1, characterized in that: The citrus is selected from London late navel orange, Newhall navel orange and summer orange.

4. The use according to any one of claims 1 to 3, characterized in that: The method further comprises: bagging or storing the citrus fruits normally after drying.

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